In a magnetic disk drive apparatus, a magnetoresistive (MR) head is positioned on a target track of a hard disk and data is magnetically read from or written onto the disk by a magnetic head. The data is embedded in the magnetic domains on the disk. The output resistance of a MR head changes as a magnetic field of the domains change. By applying a predetermined current to an MR element, the resistance change is converted to a DC voltage signal to execute data read.
The MR head is kept a slight space above the disk during the read or write operation. A thermal asperity is a protrusion on a disk which interrupts data read or write. When the thermal asperity contacts the MR head component, the strip temperature of the MR head may locally rise to 100.degree. C. or higher. The term thermal asperity thus refers to the protrusion itself and/or the phenomena of the rise in temperature. The temperature increase is caused by a mechanical collision between a head portion including an MR stripe and the protrusion on the surface of a disk. The resistance change rate of an MR head resulting from a change of a magnetic field at the time of normal read is less than one percent of an original resistance of the MR stripe. A signal change resulting from a temperature rise because of a thermal asperity greatly exceeds a resistance change due to normal read and as a consequence, normal data read is interrupted.
There are some conventional methods for protecting read data from a thermal asperity. For example, when the signal changes suddenly, probably because of a thermal asperity, the read signal is properly changed by some signal compensation method such as an error correction code (ECC). Such conventional methods, however, have some disadvantages. The thermal asperity often causes a large burst error, and the number of bits which are correctable by ECC is limited, so most errors caused by a thermal asperity cannot be corrected by ECC. Thus, errors caused by a thermal asperity have been regarded as nonrecoverable hard errors. Conventional measures, therefore, cannot be a method for completely solving the problem caused by a thermal asperity.
It is an object of the present invention to provide a disk drive apparatus and a method capable of recovering an error resulting from a thermal asperity. This invention removes a thermal asperity, then resolves the disadvantages of the above conventional thermal-asperity prevention measures.